Hydraulic brake systems are known which include a motor driven pump for pumping hydraulic fluid to a wheel cylinder. The hydraulic fluid pumped by the pump causes actuation of the wheel cylinder whereby a brake pad is urged against the brake disk to impart a braking force to the vehicle wheel. In these systems, a brake line and a hose are provided to connect the pump to the wheel cylinder so that hydraulic fluid is able to flow to the wheel cylinder. This hose is made of a compliant material which expands under the pressure of the hydraulic fluid being pumped from the pump to the wheel cylinder. When the hose expands, a volumetric increase in the hose occurs which means that the response time of the brake system is reduced since a greater volume of space in the hose must be filled with hydraulic fluid to effect actuation of the wheel cylinder. A certain amount of compliance is also associated with the brake line, although typically to a lesser degree than the flexible hose. This compliance of the brake line also contributes to reducing the response time of the braking system.
Hydraulic brake systems also possess other characteristics that introduce compliance into the brake system. For example, the hydraulic fluid utilized in the brake system typically possesses compliant characteristics to the extent the fluid is somewhat compressible. This compliant or compressible nature of the hydraulic fluid means that when the hydraulic fluid is pumped to the wheel cylinder, the fluid is compressed to at least some extent, thereby reducing the reaction time of the brake system.
Another aspect of the brake system which contributes to the creation of compliance is the brake caliper. When hydraulic brake pressure is applied to the wheel cylinder, the movable brake pad is pushed into contact with the brake disk and the brake caliper body is moved to press the other brake pad against the brake disk. During this operation, the brake caliper can experience a slight deflection or deformation. This slight deflection or deformation results in a volumetric increase behind the movable brake pad which introduces compliance into the brake system. Additionally, the initial movement of the movable brake pad introduces compliance into the system.
To compensate for these various types of compliance, either individually or collectively, and improve the response time of the brake actuation, a motor having a greater power output can be employed. However, that involves the use of a motor of rather large size which means that more space is required. Further, the larger size motor is heavier and more costly than would otherwise be the case.